Refrigerant compressor for vehicles

ABSTRACT

Compressor apparatus for use with a variable speed power plant to compress refrigerant vapor in an air conditioning system. The compressor includes a plurality of cylinders having pistons which are sequentially operated. Each of the cylinders is provided with refrigerant vapor from multiple chambers of limited capacity in communication with each other and with a plenum chamber of the compressor by metering structures so that the volume of refrigerant vapor being compressed is directly proportional to the speed of the vehicle and the condenser pressure of the system.

United States Patent Nickell Dec. 25, 1973 [5 REFRIGERANT COMPRESSOR FOR3,685,923 8/1972 Hutchins 417 273 VEHICLES 3,692,434 9 1972 Schnear417/266 [75] Inventor: Claude II. Nickell, Dearborn, Mich. FOREIGNPATENTS OR APPLICATIONS 731 Assignees: Claude H. Nickel], Deal-born;608,892 ll/l960 Canada 4I7/539 Winfred D. Weldon, Detroit; Manuel Pinko;Adam Pianga, Primary ExaminerWilliam L. Freeh Dearborn, Mich.Attorney-A. Yates Dowel], Jr.

[22] Filed: May 19, 1972 21 Appl. No.2 255,235 [57] ABSTRACT Compressorapparatus for use with a variable speed power plant to compressrefrigerant vapor in an air [2%] C(il. conditioning System. Thecompressor includes a p d 539 273 rality of cylinders having pistonswhich are sequen- 1 0 care 4111/53; tially operated. Each of thecylinders is provided with refrigerant vapor from multiple chambers oflimited capacity in communication with each other and with a [56]References cued plenum chamber of the compressor by metering struc-UNITED STATES PATENTS tures so that the volume of refrigerant vaporbeing 1,916,130 6/1933 Torrey 417/441 compressed is directlyproportional to the speed of the 2.819,678 l/l958 e" 417/571 vehicle andthe condenser pressure of the system. 3,174,436 3/1965 Wanner 417/2733,456,874 7/1969 Craper 417/534 8 Claims, 31 Drawing Figures Tn m9,

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SHEET 13 0F 15 PATENTEDUEEZS ma SHEET 15 HF 15 F/az r REFRIGERANTCOMPRESSOR FOR VEHICLES BACKGROUND OF THE INVENTION 1. Field of theInvention.

This invention relates generally to refrigeration systems of variouskinds and relates particularly to compressor mechanism used withvariable speed power plants for compressing refrigerant vapor anddischarging the same to a conventional refrigerant condenser.

2. Description of the Prior Art.

Heretofore manyefforts have been made to provide refrigerant compressorsfor use with motor vehicles such as automobiles, buses, trucks and thelike, as well as other apparatus having a variable speed power plant.The problems of efficient cooling of motor vehicles are separate anddistinct from'the problems encountered in refrigerant systems forbuildings and other structures having a constant speed power input. Anengine driven vehicle is subject to constantly and sometimes rapidlychanging conditions, including changes in weather, air currents, andchanges inspeed and direction of the vehicle. As an example, when anautomobile is idling or traveling at a slow speed, the greatest amountof compressed refrigerant vapor is required for the comfort of thepassengers of the vehicle. When the vehicle is travelingat a relativelyhigh speed, such vehicle functions as a heat exchange member since thevehicle is traveling at a rapid speed through the surroundingatmosphere. Also, at idle speeds the crankcase back pressure of thecompressor is at its highest because of the boil-off rate of theevaporator.

In most refrigerant compressors of the prior art, the vapor inlets ofthe cylinders are in direct communication with the crankcase plenumchamber so that the volume and pressure of the vapor being introducedinto the cylinders is in direct proportion to the volume and pressurewithin the crankcase. In this arrangement, rapid acceleration quicklyscavenges the vapor from the crankcase plenum chamber and therebyreduces the efficiency of the compressor while increasing the powerrequirements for operating the same.

Most vehicle compressors include a pair of generally parallel cylindershaving relatively large cross-sectional areas and the pistons withinsuch cylinders have relatively long strokes to produce the necessarycompression required by the refrigerant system. Normally, in atwo-cylinder compressor, the lobes of the crankshaft are disposed onopposite sides so that the shaft can be statically and dynamicallybalanced. In some twocylinder compressors, the cylinders are arranged ina V-shape so that the compression has not been equal. In other words,during the first portion of crankshaft rotation, the cylinders willcompress refrigerant vapor through approximately 90 of rotation of theshaft and then for approximately 270 of rotation no compressing willtake place. This creates an unbalanced condition resulting in vibrationand chatter in the compressor. Also, the first cylinder receives a fullcharge of vapor; however, the second cylinder, which is compressed 90later, may receive less than a full charge since the plenum chamber maynot have been completely recharged after the first cylinder evacuatedthe vapor therein. Some examples of the prior art are disclosed in thepatents to Scott 2,350,537, Atchison 2,759,333, and Heidorn 3,252,296.

Summary of the Invention The present invention relates to a refrigerantcompressor for vehicles including a housing having a crankshaft locatedwithin a crankcase or plenum chamber. The housing normally includes fourcylinders with two cylinders on each side and such crankshaft isprovided with two lobes or crank pins which are offset from each otherand adapted to operate pistons on opposite sides of the housingalternately. Each of the cylinders has a plurality of limited capacitychambers with the first chambers being in communication with thecrankcase plenum chamber through metered orifices or by means of athrottling valve, and the second chambers being in communication withthe first chambers through other metered orifices. The operation of thepistons causes vapor within the second chambers to be drawn into thecylinders during the suction strokes and compresses and discharges suchvapor during the compression strokes. During the compression stroke,vapor flows from the first chambers into the second chambers and fromthe plenum chambers into the first chambers.

In two modifications, the cylinders and pistons are located in agenerally horizontal housing with a pair of cylinders disposed on eachside of a crankshaft and with the cylinders on one side being offsetslightly from the cylinders on the opposite side along the length of thecrankshaft. In a third modification, the cylinders are located within agenerally V-shaped housing disposed at an angle of approximately 45 to ahorizontal plane and such cylinders are offset slightly from each otheralong the length of the crankshaft. If desired, a throttling valve canbe provided which is fully open when the condensing pressure is low andwhich operates automatically to open and close the inlet opening to thelimited capacity chambers in accordance with the pressure in thecondenser of the refrigerating system.

It is an object of the invention to provide a compressor for arefrigeration system having a variable speed power plant in which thecompressor has a plurality of cylinders with each cylinder associatedwith multiple chambers of limited capacity in communication with eachother and with the plenum chamber of the compressor by means ofrestricted orifices or by one or more throttling valves.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG.

FIG.

FIG 3.

FIG. FIG. FIG.

5 is a section on the line 5-5 of FIG. 1. 6 is a section on the line 6-6of FIG. I. 7 is a section on the line 7-7 of FIG. 1.

FIG. 8 is a section on the line 8-8 of FIG. 1.

FIG. 9 is a fragmentary enlarged section on the line 9-9 of FIG. 1.

FIG. 10 is a section similar to FIG. 9 showing the compression stroke ofthe piston.

FIG. 11 is an enlarged vertical section of a plenum chamber shield.

FIG. 12 is a section on the line 12-12 of FIG. 11.

FIG. 13 is a transverse section of a modified form of the invention.

FIG. 14 is a fragmentary section on the line 14-14 of FIG. 13.

FIG. 15 is a side elevation along the line 15-15 of FIG. 13.

FIG. 16 is a section on the line 16-16 of FIG. 13.

FIG. 17 is a section on the line 17-17 of FIG. 13.

FIG. 18 is a top plan view of a further modified form of the inventionwith the cylinders arranged in a V- shape.

FIG. 19 is a longitudinal section on the line 19-19 of FIG. 18.

FIG. 20 is a transverse section on the line 20-20 of FIG. 18.

FIG. 21 is a section on the line 21-21 of FIG. 20 illustrating theinterior configuration of the cylinder head.

FIG. 22 is a section on the line 22-22 of FIG. 20 illustrating one sideof the valve plate.

FIG. 23 is a section on the line 23-23 of FIG. 20 illustrating theopposite side of the valve plate.

FIG. 24 is a section on the line 24-24 of FIG. 20 illustrating one sideof the cylinder housing.

FIG. 25 is an enlarged fragmentary section illustrating the meteringvalve in use.

FIG. 26 is a schematic layout of a refrigerating system.

FIG. 27 is a perspective view of an offset crankshaft.

FIG. 28 is a perspective view of one of the balancing units.

FIG. 29 is a fragmentary top plan view of the crankshaft with balancingunits mounted thereon.

FIG. 30 is a section on the line 30-30 of FIG. 29.

FIG. 31 is a section on the line 31-31 of FIG. 29.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIGS. l-12 ofthe drawings, a compressor 30 is provided including a cylinder block orhousing 31. An inlet port 32 is located at the top of the housing 31adjacent to one end thereof for introducing refrigerant vapor from anevaporator E (FIG. 24) into a plenum chamber 33 within the housing. Anoutlet port 34 is provided adjacent to the other end of the housing 31for conducting compressed gasses from the housing to a conventionalcondenser C of a refrigeration system (FIG. 26).

Within the housing 31 a crankshaft 35 is provided having offset lobes orcrank pins 36 and 37 extending radially from the longitudinal axis ofthe crankshaft substantially at 90 rotation relative to each other. Asillustrated in FIG. 4, one end of the crankshaft 35 is freely rotatablymounted within the housing 31 by a roller bearing 38 or otherfriction-free member, while the opposite end of such crankshaft isfreely rotatably mounted in a bushing 39. In order to drive thecrankshaft 35, one end of such crankshaft extends through the housing 31and is keyed or otherwise connected to the hub 40 of a drive plate 41. Adrive pulley 42 is freely rotatably mounted on the hub 40 and suchpulley includes a sheave 43 adapted to receive a V-belt (not shown)driven by the crankshaft of the vehicle engine.

-A conventional electromagnetic or other clutch 44 is provided forselectively drivingly connecting the drive plate 41 to the drive pulley42 in a conventional manner when desired. It is contemplated that thecrankshaft 35 could be driven directly from the engine crankshaft bymeans of a pair of universal joints. Such direct drive could eliminatepeak loading of the V-belt as well as belt jerk, high torque peaks andhigh starting torque.

The housing 31 is provided with a pair of horizontally disposedcylindrical bores 48 on each side of the crankshaft 35 and each of suchbores has a liner or sleeve 49 forming a cylinder 50 which slidablyreceives a piston 51. Each piston has a wrist pin 52 on which one end ofa connecting rod 53 is swingably mounted. The opposite end of eachconnecting rod is attached to an insert bearing 54 rotatably mounted onone of the lobes 36 or 37 of the crankshaft 35. As illustrated in FIG.4, a nair of connecting rods 53, extending toward opposite sides of thehousing 31, are rotatably mounted on each of the lobes 36 and 37. Sincethe lobes are disposed at an angle of substantially 90 to each other,one of the pistons will fully compress a charge of refrigerant vaporevery 90 of rotation of the crankshaft 35.

In order to introduce refrigerant vapor to be compressed into thecylinders 50, the housing 31 is provided with an inwardly extendingrecess defining a generally C-shaped chamber of limited capacity 55extending partially around each of the cylinders 50. Each of thechambers 55 is in communication with the plenum chamber 33 through arestricted or metering orifice 56 in the wall of the housing 31.Preferably a shield 57 is disposed in front of each of the orifices 56and each shield has an inclined opening 58 to permit free access ofrefrigerant vapor from the plenum chamber 33 into the orifice 56. Theopenings 58 are inclined so that any oil entrained in the regrigerantvapor and which condenses on the walls of the shield 57 will drain backinto the plenum chamber.

The crankshaft 35 includes one or more counterweights 59 for lubricatingthe pistons 51 and other moving parts within the compressor housing andthe shields 57 prevent droplets of oil from being thrown directly intothe orifices 56. A pool or supply of oil maintained in an oil pan 60 atthe bottom of the housing 31 at all times to reduce frictional wear onthe moving parts.

A valve plate 61 is located exteriorly of the housing 31 adjacent to thecylinders 50 and a cylinder head 62 is mounted on the opposite side ofthe valve plate and connected to the housing 31 by a plurality of boltsor other fasteners 63. Each cylinder head 62 includes a generallyC-shaped recess or pocket defining a chamber of limited capacity 64extending partially around each of the cylinders 50 and each of suchchambers is in communication with the corresponding chamber 55 of thehousing by means of a restricting or metering orifree 65 extendingthrough the valve plate 61. The orifices 65 are located adjacent to thebottom of the valve plate 61 and if desired an oil bleed hole 66 mayprovide communication between the chamber 55 and the chamber 64 adjacentto the upper portion of the valve plate.

As illustrated best in FIG. 5, the cylinder head 62 has an imperforaterib 67 disposed along the lower portion of the vertical axis of the headto separate the chambers 64. The rib 67 is connected to an imperforatewall 68 defining a pair of recesses or pockets 69 substantially inalignment with the cylinders 50. Such pockets 69 are in communicationwith each other and with a channel 70 formed by the wall 68. The channel70 on each side of the compressor communicates with the outlet port 34through passageways 71 formed in the housing 31.

A plurality of bosses 72 are located within the chambers 64 throughwhich the fasteners 63 extend. As illustrated, the bosses are connectedby ribs 73 to the wall 68 and by ribs 74 to side walls 75 of the cap.The ribs 74 do not extend the full length of the bosses 72 to providefor free flow of vapor fluid within the chambers 64.

The valve plate 61 is provided witha plurality of angularly disposedopenings or orifices 76 providing communication between the chamber 64and the interior of the cylinder 50. A flexible disk valve 77 is mountedby a' fastener 78 on the inner side of valve plate 61 and within thecylinder 50 so that when the piston 5 ll is retracted, the suction 01"negative pressure created within the cylinder will open the disk valveand permit refrigerant vapor to flow from the chamber 64 into thecylinder. The orifices 70 are located on a generally C- shaped boltcenter disposed within the chamber 64 so that vapor within the recess 64only can be drawn into the cylinder.

A plurality of orifices 85 extend through the valve plate 61 and providecommunication between the cylinder 50 and the pockets 69 in the cylinderhead 62. A disk valve 86 is mounted on the exterior of the valve plate61 and within each pocket 69 to normally close the orifices 83. A buffer87 having an inclined face 88 is mounted on the fastener 78 within thepockets 69. The inclined face 88 permits the disk valve 86 to open alimited amount when the vapor within the cylinder has been compressed todischarge the compressed gas into the pocket 69 and through the channel70 and passageways 71 to the outlet port 34.

Pressure within the plenum chamber 33 forces oil from the oil pan 60upwardly through a screen and oil tube 90 and into an oil line 91 whichdischarges such oil into a passage 92 extending generally centrally ofthe crankshaft 35. If desired, an oil pump (not shown) could be providedto receive oil from the oil pan 60 and pump such oil under pressure intothe passage 92. An oil port 93 extends from the passage 92 to each ofthe connecting rod bearings 54 for lubricating such bearings. Asillustrated in FIG. 4, the insert bearings 54 have openings 94 and theconnecting rods 53 have a central bore 95 in alignment with one of theopenings 94 for lubricating the connection between the outer end of theconnecting rods and wrist pins 52.

A rotary shaft seal 96 is carried by the crankshaft 35 and such sealbears against an insert 97 carried by the housing 31 to prevent oil orvapor from within the housing from seeping out along the crankshaft. Inorder to lubricate the shaft seal 96, an oil port 98 extends outwardlyfrom the passage 92 to the area surrounding the seal 96. Normally theroller bearing 38 is provided with a pair of shields 99 which interruptthe flow of oil from the seal 96 back to the oil pan 60- To permit thepassage of oil from the seal 96, as well as to lubricate the rollerbearing, each of the shields 99 is provided with one or more openings100 which permit oil to flow from the area of the shaft seal through theroller bearing 38 and back to the oil pan.

in the operation of this modification of the device, refrigerant vaporenters the inlet port of the compressor 30 from the evaporator E. Suchvapor is under pressure or back pressure from the evaporator andcompletely fills the plenum chamber 33 above the level of the oil in theoil pan 60. Refrigerant vapor passes through the opening 58 in each ofthe shields 57 and through each of the restricted orifices 66 into thelimited capacity chambers 55. From the chambers 55, the vapor passesthrough orifices 65 into the limited capacity chambers 64 within thecylinder head 62. As long as the compressor is not operating, thepressure of the vapor within the plenum chamber 33 and the chambers 55and 64 will reach equilibrium with the crankcase back pressure. If thevapor pressure within the chambers 64 is great enough to unseat the diskvalves 77, then the cylinders likewise will be filled with vapor. Whenthe clutch 44 is energized, the crankshaft 35 is rotated by the drivepulley 42 to cause the pistons 51 to be reciprocated within thecylinders 50. One of the pistons 51 is fully closed every 90 of rotationof the crankshaft 35 and when one piston is in closed position, theother piston on the same crankshaft lobe is in fully open position. Thepistons on the other lobe are in intermediate positions, one beingmidway through the suction stroke and the other midway through thecompression stroke.

The lobes 36 and 37 of the crankshaft are offset only a short distanceof approximately one-half inch so that the stroke of the pistons 51 isrelatively short and the surface speed is slower in feet per minute thanconventional compressor pistons and, therefore, vibration and rockingaction are substantially reduced. At an idling speed of approximately600 rpms, the back pressure from the evaporator is greatest and therefrigerant vapor is forced into the chambers and 64 as rapidly aspossible. At this time, the pistons 51 are reciprocating at theirslowest speed and as each piston is retracted, vapor is withdrawnthrough the orifices 76 and the disk valve 77 into the cylinder. At theend of the suction stroke, the disk valve 77 closes the orifices 76 sothat when the direction of movement of the piston 51 is reversed on thecompression stroke, the vapor within the cylinder is compressed. Duringthe compression stroke when the vapor within the cylinder reaches thehead pressure, the disk valve 86 opens and vapor under pressure isdischarged from the cylinder through the orifices 85 into the pockets 69from which the compressed gas flows through the channel 70, passageway71, and through the outlet port 34 to the condenser.

When the engine of the vehicle is accelerated, the back pressure withinthe plenum chamber 33 is reduced and simultaneously the pistons 51 whichare moving more rapidly quickly scavenge the vapor from the chamber 64.Due to the reduced pressure within the plenum chamber, and therestricted orifices 56 and 65, the amount of vapor which can flow intothe chamber 64 during the compression stroke of the piston is limited,such amount being a factor of time, pressure, and capacity of vaporwhich can flow through the orifices, as well as the pressure of thevapor within the plenum chamber. The metered orifices 56 and aredesigned to supply the greatest amount of fluid to the cylinders 50 atidle or low speeds and variations of the crankcase back pressure androtational speed of the. crankshaft automatically change the outputvolume and pressure at the outlet port 34. When the vehicle speedincreases, the demand for refrigerant decreases thereby cutting down theoutput of the compressor which permits high speed driving for longperiods of time.

With reference to FIGS. 13-17, a modified form of compressor isillustrated including a housing 104 having a plenum chamber l05-with acrankshaft 35 rotatably mounted therein. The housing 104 includes a pairof horizontally disposed bores 106 on each side in which liners 49forming cylinders 50 are mounted. Each of the cylinders slidablyreceives a piston 51 connected by a wrist pin 52 to one end of aconnecting rod 53, as previously described. The opposite end of eachconnecting rod is rotatably mounted on one of the lobes of thecrankshaft 35. An oil pan is mounted on the bottom of the housing 104 tosupply lubricant for the pistons 51 through the oil passage 92 in thecrankshaft 35. If desired, the housing 104 may have recesses 107 locatedadjacent to the lower portion of the bores 106 to provide for anincreased oil capacity.

In order to introduce refrigerant vapor into the cylinders 50, thehousing 104 is provided with a recess defining a chamber of limitedcapacity 108 extending partially around each of the cylinders 50. Inthis modification, each of the chambers 108 is connected by passageway109 to a central manifold chamber 110 communicating with the plenumchamber 105 of the hous ing by a bore 111. Preferably a shield 112 isdisposed across the open end of the bore 1 11 and such shield has aninclined passageway 113 which permits free access of refrigerant vaporfrom the plenum chamber 105 to the bore 111. The shield 112 prevents oilfrom being thrown by the crankshaft oil slingers 59 directly into thebore 111.

A valve plate 115 is located at each side of the housing adjacent to thecylinders 50 and a cylinder head 116 is mounted on the opposite side ofeach valve plate and is connected to the housing 104 by a plurality ofbolts or other fasteners 117. Each cylinder head 116 includes agenerally C-shaped recess defining a chamber of limited capacity 118extending partially around each of the cylinders 50 and each of thechambers 118 is in communication with the corresponding chamber 108 ofthe housing by means of a plurality of orifices 119 extending throughthe valve plate 115. The orifices 119 provide substantially free flow ofrefrigerant vapor from the chamber 108 to the chamber 118 at slow andidling speeds, but restrict flow of vapor at high speed because of thelesser demand.

As illustrated best in FIG. 16, the cylinder head 116 has an imperforaterib 120 disposed along the lower portion of the vertical axis of thehead to separate the chambers 118. The rib 120 is connected to animperforate wall 121 extending most of the way around the cylinders 50and define a pair of pockets 122 substantially in alignment with suchcylinders. The pockets 122 are in communication with each other by meansof a channel 123, which, in turn, communicates through a bore 124 in thevalve plate 115 with a passageway 125 in the housing 104. The passageway125 leads to a pressure dome or collector chamber 126 forming an upwardextension of such housing. The pressure dome is closed by a cap 127 andis in communication with the condenser C of the refrigerating system byan outlet line (not shown).

The valve plate 115 has a plurality of angularly disposed openings ororifices 76 providing communication between the chamber 118 and theinterior of the cylinder 50 and a plurality of orifices 85 .providingcommunication between the cylinder 50 and the pockets 122 of thecylinder head. Disk valves 77 and 86 are mounted on the valve plate 115in the same manner as previously described with reference to valve plate61 to control the flow of vapor into and gas out of the cylinder 50.

It is desirable to begin compression of refrigerant vapor as soon as thecompressor is started in order to build up pressure within the condenserC and to control the amount of vapor or gas being compressed when thecondenser pressure rises to a predetermined level. To do this, athrottling valve 130 is provided including a valve housing 131 forming apart of the housing 104 and extending upwardly into the pressure dome126. The.valve housing 131 has a bore 132 and a counterbore 133extending therethrough with the bore 132 being open to the manifoldchamber 110 and in axial alignment with the bore 111. A valve 134 islocated within the counterbore 133 and such valve has a stem 135projecting downwardly through the bore 132. A series of bellvillesprings or other resilient means, such as a calibrated coil spring 136,is disposed between the valve 134 and the bottom of the counterbore tourge the valve stem 135 away from the bore 111.

Preferably the end of the valve stem 135 remote from the valve 134 ishollow for at least a portion of its length and is provided with one ormore orifices 137 providing communication between the hollow interior ofthe stem and the manifold chamber 110 so that the flow of vapor cannotbe entirely interrupted. As illustrated in FIG. 13, the cap 127 of thepressure dome is provided with a recess 138 in the area of the upper endof the valve housing 131 so that gas under pressure within the pressuredome will have free access to the upper surface of the valve 134.

With reference to FIGS. 18-26, another modified form of the invention isdisclosed including a compressor housing having a crankcase or plenumchamber 151 in which a crankshaft 152 is rotatably mounted. In thismodification, the housing is substantially V-shaped in cross-section andincludes a pair of bores 153 on each side with each of such bores beingdisposed at an angle of approximately 45 to a horizontal plane. Each ofthe bores 153 is provided with a liner 49 defining a cylinder 50 inwhich a piston 51 is reciprocably mounted. Each piston 51 is connectedby a wrist pin 52 to one end ofa connecting rod 53 and the opposite endof such connecting rod is rotatably mounted on bearings 54 mounted onlobes 154 and 155 of the crankshaft 152.

The lobes 154 and 155 are offset from opposite sides of the central axisof the crankshaft 152 so that such lobes are substantially 180 apart.One connecting rod from each side of the housing is connected to each ofthe crankshaft lobes so that when one piston carried by the lobe 154 isfully open, as illustrated in FIG. 20, the piston of the otherconnecting rod carried by the same lobe will be in an intennediateposition. Simultaneously, one of the pistons carried by the lobe 155will be fully closed while the other piston will be in an intermediateposition. When the crankshaft is rotated, the piston which is fully openbegins to close, the piston which is fully closed begins to open, andthe two intermediate pistons move toward open and closed positions,respectively.

Refrigerant vapor from the evaporator E is introduced through an inletpassage 156 into the plenum chamber 151 and such vapor flows through abore 157 into a central manifold chamber 158. Preferably a shield 159having laterally extending passageways 160 is located across the end ofthe bore 157 to prevent oil

1. In a compressor for use with a variable speed power plant, saidcompressor having a housing with at least one cylinder, a pistonreciprocably mounted within said cylinder, means for reciprocating saidpiston, and means for discharging compressed vapor from said compressor;the improvement comprising a plenum chamber within said housing forreceiving all of the vapor to be compressed, a first chamber of limitedcapacity spaced from and communicating with said plenum chamber, firstflow control means for controlling the flow of vapor from said plenumchamber to said first chamber, a second chamber of limited capacityspaced from and communicating with said first chamber, second flowcontrol means for controlling the flow of vapor from said first chamberto said second chamber, and valve means selectively providingcommunication between said second chamber and said cylinder, wherebysaid first and second chambers and said first and second flow controlmeans provide a flow responsive control to the inlet for the cylinder sothat the suction stroke of the piston causes said valve means to openand causes vapor from said seconD chamber to flow into said cylinder andvapor from said first chamber to flow into said second chamber and vaporin said plenum chamber to flow into said first chamber, and thecompression stroke of said piston causes the vapor in said cylinder tobe compressed and discharged through said discharging means.
 2. Thestructure of claim 1 in which said first flow control means includes arestricted orifice.
 3. The structure of claim 1 in which said first flowcontrol means includes throttling valve means.
 4. The structure of claim1 in which said second flow control means includes a restricted orifice.5. The structure of claim 1 in which said housing includes a pluralityof cylinders, each of said cylinders having independent first and secondchambers of limited capacity and first and second flow control meansproviding communication with said plenum chamber.
 6. The structure ofclaim 5 in which said housing includes a plurality of cylinders disposedon opposite sides of the longitudinal axis of said housing.
 7. Thestructure of claim 6 in which the axes of said cylinders aresubstantially coplanar.
 8. The structure of claim 6 in which the axes ofthe cylinders on one side of said housing are disposed at an angle tothe axes of the cylinders on the other side of said housing.